1991 SAAB 9000

I have a 91 Saab 9000 CD I am having a problem keeping the car running. It starts fine in the morning and will run for about 10-15 minutes then dies. The car will sometimes restart but will not stay running for more than several minutes. If I let the car sit for several hours it will restart and run again but only for about 10-15 minutes. I have only had the car for about six months. When I got it I did a basic tune up replacing sparkplugs, fuel filter, etc. The car overheated on me once and the proplem was a fried balast resistor on the cooling fan. I replaced it and have not had any problems since. I have no idea if the overheating of the car has some how caused this new problem. Any help would be greatly appreciated.